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As an aside (Envite's answer is fine), be careful when saying "tu madre." Nobody reasonable would take offense at it, but not everybody is reasonable. You could get yourself into an uncomfortable spot if you say it to the wrong person. It is far more common, at least in Mexico, to say "tu mamá."
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Michael WolfMay 2 '14 at 20:44

1 Answer
1

In Spanish, since the words are properly modified (the verb is conjugated, and the names and adjectives are coordinated), there is some elasticity to order them.

This is usually done for stylistic purposes, but can be done also for meaning reasons.

¿Por qué es vendedora tu madre?

This one stresses the fact that she is a seller. Would roughly be "She is a seller. Why?"

¿Por qué es tu madre vendedora?

This one stresses the fact that the asker talks about your mother. Would roughly be "Let's talk about your mother. Why is she a seller?"

¿Por qué tu madre es vendedora?

This one follows the standard order of words in Spanish: subject "tu madre", verb "es", predicate "vendedora"; so it does not stress anything in particular. This one is the standard way of asking this question in most Spanish-speaking places. But note that there are regional differences.